The short answer is no.
The chemical nature of the Shroud image has not been resolved as a settled scientific fact—at least not in the sense of a broad consensus shared by all researchers, from skeptics to believers. Instead, what we have is a decades-long debate, often resembling a quiet “cold war” between competing interpretations.
At its core, the disagreement has centered on two main approaches: a pigment-based explanation and a chemical alteration of the linen itself.
1. The McCrone Findings: The “Painting” Hypothesis
Walter McCrone, a highly respected microscopist and member* of the 1978 Shroud of Turin Research Project (STURP), reached conclusions that sharply diverged from the rest of the team.
The claim:
Using tape-lift samples, McCrone identified particles he interpreted as iron oxide (red ochre) and vermilion (mercuric sulfide).
The conclusion:
He argued the image was created by a medieval artist using a dilute tempera paint—pigment suspended in a protein binder.
Why it matters:
McCrone’s work remains a cornerstone for skeptical interpretations because it offers a straightforward, material explanation: the image is painted. His book is in print, and the Chicago-based firm he created stands by his work in the forensic science marketplace.
2. The STURP Position: The “No-Paint” Conclusion
Other STURP scientists—notably Raymond Rogers and Alan Adler—disagreed with McCrone’s interpretation.
The claim:
While acknowledging that pigments exist on the cloth (likely from centuries of handling and contact with painted copies), they argued these are not responsible for the image itself.
The conclusion:
The image is not a material applied to the cloth. Instead, it reflects a chemical change in the linen fibers—specifically, an oxidative dehydration of the cellulose. In effect, the outermost fibers (only a few micrometers deep) appear discolored or “aged.”
Why it matters:
STURP concluded that the image could not be explained by known artistic techniques—and famously described it as a scientific mystery.
3. The Maillard Reaction: A Possible Middle Ground
In later work, Raymond Rogers proposed a more nuanced explanation that has gained attention.
The idea:
A Maillard reaction—similar to the browning of food—occurring between reducing sugars (possibly from a starch coating on the linen) and amine vapors from a body.
The result:
A thin, straw-colored discoloration on the surface of the fibers, consistent with the superficiality and chemistry observed, without requiring either paint or extraordinary radiation-based mechanisms.
Why it matters:
This proposal attempts to bridge the gap: a natural chemical process that could account for many observed features while avoiding both the “painting” and “miracle” extremes.
4. Intaglio Possibility
It is also worth noting that Joseph Accetta, an original member of the STURP team, proposed that known medieval techniques—such as woodblock or intaglio methods—could plausibly account for many of the Shroud’s visible features, including its negative-like appearance and even its response under VP-8 analysis.
However, Accetta’s proposal was primarily a plausibility argument at the level of image formation, not a complete solution. He did not provide a detailed chemical mechanism or a full replication matching the fiber-level characteristics identified by STURP. As such, his work usefully challenges claims of uniqueness, implies an applied substance such as ink, but does not resolve the broader question of how the image was actually formed.
Where Things Stand
More recent analytical techniques (including advanced X-ray studies) have added further data points—some suggesting an older origin for the linen itself—but they have not resolved the central question of how the image was formed.
So where does that leave us?
In simplified terms:
- McCrone argued that there is paint on the Shroud.
- STURP argued that the image is not made of paint.
Those two statements are not mutually exclusive—and both may contain elements of truth.
The Bottom Line
The chemistry of the Shroud image is not settled science. It remains an open question, shaped by competing interpretations of complex and limited data.
What is clear is this: the image does not fit neatly into any single, universally accepted explanation. And until it does, the debate is likely to continue.
*McCrone’s formal membership in STURP is a matter of some dispute. What is not disputed is that Raymond Rogers, STURP’s lead chemist, supplied him with tape-lift samples for analysis.
Hi, Dan,
It’s late where I’m at–3:18 am to be exact–so just a quick response before I go to get some sleep. Sure, there’s paint on the Shroud of Turin–going from memory here, there’s a bit of rose madder, orpiment, I think some ultramarine blue and perhaps a few other colors. But, that’s just from contact transfer with either some of the approximately 50 documented painted COPIES of the Shroud that had been touched to the authentic Shroud so that they could become sanctified and turned into 3rd class relics by way of having made contact with a first-class relic (the genuine Shroud of Christ/Shroud of Turin.) But, flecks of paint due to contact transfer do not account for the images that are SEEN. We’ve discussed the Beer-Lambert law here many, many times. If something is said to be a painting, then there needs to be a corresponding amount of paint to account for the image that is seen. Aside from the microscopy that has been performed and the chemical and physics-based tests, we know that the best explanation is that there is simply cellulosic yellowing that has occurred from (almost certainly) accelerated aging due to Resurrection Energy. The aforementioned tests have ruled out the presence of paint, pigment, stain and dye. Even most of the toughest skeptics (including your favorite–Hugh Farey–but, also, people like Dan McClellan and (if I recall correctly, James Fodor and that other guy who wears a bow tie–is he on the show “Reason to Doubt”)–they all agree that the body images are due to cellulosic yellowing.
McCrone doesn’t get to rest on his laurels when it comes to his errors concerning the Shroud, and we’ve discussed this so many times here on both your website and Hugh’s. Initially, he erred because he only examined the fibers via microscopy and examined the specimens through the the optically active tape. This threw off the results and made it appear that he was examining iron-oxide. Then, despite evidence to the contrary, he just doubled down on that (at least to the public) to the very end of his life.
Dear Dan,
You are right to emphasize that the chemistry is not fully resolved. However, the fault lines you identify do not correspond to the actual points of contention in current Shroud research. Allow me to offer several clarifications.
1. STURP did not settle on a cellulose‑degradation model
Your presentation of STURP’s early (1981) hypothesis – often described as oxidative dehydration of cellulose – treats it as though it represents their final position. It does not. Subsequent work by Raymond Rogers, STURP’s lead chemist, led him to reconsider that interpretation using STURP’s own adhesive tape samples.
Two observations are particularly relevant. First, treatment with diimide reagent removed the image coloration, leaving behind colorless fibers that appeared structurally intact. While not logically decisive on its own, this behavior is difficult to reconcile with a model in which the cellulose itself has undergone substantial chemical transformation, and is more consistent with a reducible surface chromophore. Second, when image fibers were mechanically lifted from adhesive tapes, residual colored “ghosts” were left behind on the tape, while the fibers themselves appeared largely colorless. This is difficult to explain under a bulk‑cellulose model and is more consistent with a chromophore that behaves as a separable surface component rather than an intrinsic modification of the fiber.
On this basis, Rogers concluded that the image likely resides in a thin layer of impurities on the fiber surface – identified as a carbohydrate‑rich coating, plausibly including starch fractions supported by iodine microchemical tests—rather than in the cellulose itself. Whether or not one accepts this conclusion in full, it represents a serious reinterpretation grounded in STURP data and should not be conflated with the earlier cellulose‑degradation model.
2. The real unresolved question: coating vs. cellulose
You are correct that the chemistry is unsettled, but the live question is more specific than your framing suggests. The central issue is not “paint vs. no paint,” but whether the chromophore resides in a superficial carbohydrate coating on the fibers (Rogers’ model) or in the outermost layer of the cellulose itself, modified by photochemical or thermal processes.
The ENEA laser experiments (Di Lazzaro et al., 2010–2015) are relevant here. They demonstrate that deep‑UV nanosecond pulses can produce extremely superficial coloration on linen, with penetration depths on the order of a few hundred nanometers and optical properties resembling those of the Shroud image. These results show that a cellulose‑based photochemical pathway is chemically possible.
At the same time, the ENEA experiments do not constitute a full reproduction of the Shroud image. They do not account for large‑scale image formation, anatomical mapping, or the spatial encoding observed on the cloth – nor were they designed to. In particular, they address coloration mechanisms, not the formation of a full‑body image with encoded spatial information. Nor do they directly address the evidence cited by Rogers for a separable surface chromophore (the ghost‑fiber behavior and diimide reduction). Accordingly, the present state of the question is not resolved but narrowed: competing models exist, each with some experimental support, and neither has yet achieved explanatory completeness.
3. The Maillard reaction is a leading candidate, not the only one
Rogers proposed that the carbohydrate coating colored via a Maillard reaction (amine vapors reacting with reducing sugars). That remains a plausible and well‑developed mechanism, but it is not the only possible pathway. The same carbohydrate‑rich surface layer could, in principle, undergo coloration through caramelization (thermal degradation) or other oxidative processes. The key point is that a surface impurity layer is supported by microchemical evidence; the specific reaction pathway responsible for the observed chromophore remains an open question.
4. McCrone and STURP are not epistemically equivalent
You suggest that McCrone’s painting hypothesis and STURP’s no‑paint conclusion “may both contain elements of truth,” implying a rough equivalence. This characterization requires qualification. Both McCrone and STURP detected iron oxide on the cloth. The disagreement concerns its origin and distribution. STURP’s X‑ray fluorescence measurements indicated that iron is present across both image and non‑image areas at levels consistent with background contamination associated with linen processing. This distribution is not what one would expect from a deliberately applied pigment, which would be concentrated in image‑bearing regions. McCrone’s identification of iron oxide particles was methodologically sound; however, his inference that they constitute a painting medium remains disputed. The issue is therefore not symmetrical: the presence of iron oxide is not in question, but its interpretive significance is.
5. A note on the intaglio proposal
Your article mentions Joseph Accetta’s suggestion that intaglio or woodblock methods could account for the Shroud’s visual features. It is worth noting that such proposals address the macroscopic pattern of the image, not its chemistry. They do not provide a chemical mechanism nor replicate the fiber‑level characteristics identified by STURP (including extreme superficiality, absence of a binder, and specific spectral properties). As such, they remain speculative without corresponding chemical support and do not resolve the coating‑versus‑cellulose question.
6. Where the real questions remain
If the image resides in a surface coating, an important unresolved issue is whether a Maillard‑type reaction driven by amine vapors can account for the observed spatial resolution and tonal gradation, given the expected diffusion behavior of reactive gases. This remains a substantive challenge for Rogers’ model. If, instead, the image reflects direct modification of the cellulose surface, the key question becomes the nature of the energy source required to produce such a superficial and spatially resolved effect. The ENEA team themselves noted that no currently available natural or technological source readily accounts for the required combination of intensity, wavelength, and uniformity, though the underlying physics does not forbid such processes. These are narrower, chemically specific questions. They represent the actual frontier of inquiry, rather than a continuation of the older “paint vs. no paint” debate.
Your article is correct to state that the chemistry of the Shroud image is not settled. However, the structure of the debate has shifted. It is no longer primarily about whether McCrone’s paint hypothesis or an early STURP cellulose‑degradation model is correct. Rather, the central question is whether the image resides in a separable surface coating (as proposed by Rogers) or in a modified cellulose surface (as suggested by photochemical models), and in either case, what specific chemical pathway and energy source can account for the full set of observed features. I hope these clarifications help sharpen the discussion and focus attention on the questions that remain genuinely open.
I really don;t know where the debate has shifted. I recognize your expertise there. My point is that the matter is not settled. And I don;t believe it will be settled without more roll-up-the-sleeves research.
BTW: This is the entry for your book in the For Further Reading section of my forthcoming book “Our Hunger for Signs: The Shroud of Turin as a Case Study” (working title for now), a book in which I do not argue the science or the history or take a position on authenticity.
The Shroud of Turin: A Forensic Summary of the Evidence by Otangelo Grasso (2024 & 2026). The most comprehensive recent forensic case for the Shroud’s authenticity currently available, covering textile analysis, blood chemistry, wound forensics, image physics, and the radiocarbon dating controversy across twenty-two chapters. Grasso writes as a committed advocate for authenticity, and the reader should receive it as such — but the breadth of evidence he assembles and the seriousness with which he engages counterarguments make this a valuable resource for anyone who wants to understand the pro-authenticity case in its fullest contemporary form.
Hi, Otangelo,
You state the following: ” McCrone’s identification of iron oxide particles was methodologically sound.”
This is totally incorrect.
It is, in fact, McCrone’s flawed, methodologically unsound way of attempting to identify the particles (particularly the reddish ones) on the Holy Shroud that caused him to first mistake blood for iron-oxide. He made the mistake (which Heller and Adler did not) of examining the fibers and the particles on the fibers while they were still attached to the OPTICALLY ACTIVE sticky-tape. The optical activity of the sticky-tape (which McCrone was using like a cover glass on top of the microscope slides) ended up making non-birefringent, isotropic blood appear as if it was birefringent, anisotropic iron-oxide in the form of hematite. McCrone then declared his finding at a STURP conference. When Heller asked him how he made this conclusion, McCrone specified his method, and then it was clear how the “Father of Modern Microscopy”–who many viewed as being akin the the “unsinkable Titanic”–made a blunder that is comparable to the bundle of errors that resulted in the Titanic’s sinking. Had the man had any integrity and honor, he could have just admitted that he had “rushed to judgment” and failed to properly examine the particles so as to get a correct analysis of them, but his ego was too big to allow himself to fail–especially with so many eyes watching. That’s shameful.
Best regards,
Teddi